SNMP Traps are packets containing one or more parts of information sent by an agent to a dedicated listening device via the Simple Network Management Protocol (SNMP).

With the SNMP Trap Receiver sensor you can configure any PRTG probe device as a trap receiver. The sensor checks every interval if new traps have been received and reports the number of traps received so far in its primary channel.

These are the differences between a dedicated trap receiver and PRTG's trap receiver:

• Dedicated trap receivers are optimized to receive and process many different traps from a large number of devices.
• Dedicated trap receivers are able to store many messages per time interval in their internal database for later analysis.
• PRTG's trap receivers are not suitable to handle high loads, process many different message types or to store many messages in its log database. It can process some hundred messages per minute, one sensor can process and check one message type and PRTG can store some hundred messages per minute in its log database (across all trap sending agents).

The sensor is not intended to be a full-scale replacement for a dedicated trap receiver. It is a great tool if you need to monitor a handful of devices that send traps from time to time. And, as such, it avoids the need to install, setup and manage a dedicated trap receiver software for just a few devices.

Configuring a SNMP trap sensor

To create a SNMP trap sensor navigate to your "local probe" (or one of your remote probes) and choose "Add Sensor". From the sensor type selection menu choose "SNMP Trap Receiver" under the "Various Protocols" section.

In the sensor settings you must enter a listening port (the common port number is 162).

Note: Remember that the listening port must be opened if you run a firewall on the probe system (the built-in Windows Firewall will be configured automatically by PRTG).

Note: You can only create SNMP trap sensors on probe devices, seeing as the PC running the probe software is the actual receiver.

The SNMP Trap sensor has four other settings:

• OID value: SNMP traps sent by agents may contain several different textual information entries, each represented by a unique OID. It is therefore necessary to tell PRTG which part of the trap you want to log. Please refer to the trap sending device description to find the appropriate OID.

• When a message comes in: Activate the option "Write message to log and fire change trigger" to fire the "change trigger" for this sensor and to write a log entry whenever a trap is received (this may create lots of log entries, use with caution). This is only suitable when a few messages per minute are received. After creating the sensor you can enter a "change" trigger on the notifications tab of the sensor that will send a notification (e.g. email) whenever a trap comes in.
• Message must include: This setting allows you to define a string. The sensor will go into error state if one or more of the incoming messages do not contain this string.
• Message must not include: Here you can enter a second string. The sensor will go into error state if a message contains this string. The first option allows you to create a log of all incoming messages (at least for small scenarios with <100 messages per minute).

The 2nd and 3rd option are used to filter out specific messages. Configure a "state trigger" for "down" on the notification tab and PRTG will trigger an email if a message meeting any or both of the two criteria is received.

See Also

• How do I find out what OID I need to use for a custom sensor?
• How do I test an SNMP Trap Receiver Sensor?